This invention relates to a sealing structure for a mechanism such as an automobile engine in which a movable part such as a crankshaft passes through a structural component such as an engine block and must be sealed against leakage of fluid such as oil.
FIG. 8 shows a conventional sealing structure for use in an automobile engine. A sealing assembly A' includes a metal retainer 101, a lip 102, a shaft 106 and an engine block 107 ran engine body. The lip 102 is formed of a rubber material as to be integral with the retainer 101 as a seal lip. The retainer 101 is fixed to the engine block 107 by means of bolts 111 and has a groove 109 in which an O-ring 110 is arranged for the purpose of oil seal between the retainer 101 and the engine block 107. The lip 102 has a main lip portion 102a which contacts an outer peripheral portion of the shaft 106 in a slidable manner, and an auxiliary lip portion 102b which is formed outside the main lip portion 102a and positioned so as to face the atmosphere. The retainer 101 has a joint portion 101a at an inner peripheral portion thereof, to which the lip 102 is joined in a fixed manner. Thus, the retainer 101 and the lip 102 are assembled as an integral unit. A spring 105 is placed on an outer peripheral portion of the main lip portion 102a for the purpose of adjusting a pressure of the main lip portion 102a against the shaft 106.
However, in the conventional sealing structure, when heat is transferred from the engine block 107 to the retainer 101, the retainer 101 is deformed so as to deform further the lip 102. In case the retainer is made of a resin material, it is apt to be remarkably deformed, and the lip is affected by such deformed shape of the retainer which takes place when the resin material is shaped and then solidified. In such a case, a gap is formed between the outer periphery of the shaft 106 and the main lip portion 102a, and the contact therebetween is biased so as to result in an abnormal one. As a result, the sealing structure has poor sealing characteristics so that oil leakage may take place.